The aromatic carbonate polymers, also referred to as aromatic polycarbonate resins, are a well known family of available materials which enjoy a variety of applications. These polymers are characterized by good ductility in thinner sections, manifesting high impact strength in articles molded or otherwise shaped from the polymer or blends of the polymer. However, in certain applications where thicker sections are desired, the use of aromatic polycarbonates is limited because the ductility and the impact strength tend to decline with increasing average thickness. As is also known, these resins sometimes exhibit environmental stress crazing and cracking, which is a type of mechanical failure hastened by organic solvents when such solvents are brought into contact with stressed parts fabricated from the resin.
It has been proposed that the resistance of aromatic polycarbonates to environmental stress crazing and cracking can be improved by admixing the polymer with polyolefins and olefin copolymers. Blends of that kind are disclosed by Goldblum in U.S. Pat. No. 3,431,224. In practice, however, it has been found that the use of polyolefins in blends with aromatic polycarbonates is somewhat limited, especially when gasoline resistance is important. More specifically, when the polyolefins are incorporated in levels which are high enough to achieve the desired advantage of improved stress cracking/crazing resistance, there is a tendency for the molded part to delaminate due to the immiscibility or incompatibility of the two materials.
In applicant's U.S. Pat. No. 4,245,058, compositions are described comprising an aromatic polycarbonate, up to 4 parts by weight of a polyolefin per 100 parts by weight of polycarbonate and polyolefin combined, and a modifying amount of an acrylate copolymer, the latter being in an amount sufficient to induce a desirable ductile mode of failure on impact. There is no suggestion in the patent that higher amounts of polyolefin might be tolerated without shifting over into a brittle mode of failure, and no mention at all that the acrylate copolymer might enhance environmental stress cracking and crazing resistance, especially gasoline soaking resistance, of compositions comprising polycarbonates and substantial, i.e., greater than 10 parts by weight, contents of polyolefins, per 100 parts by weight of polycarbonates and polyolefins, combined.